Abstract

Acquired digital fibrokeratomas (ADF) are benign and uncommon lesions consisting of collagenous papules and nodules covered
by hyperkeratotic epidermis. These tumors occur mainly on the fingers and toes and infrequently on the palms and soles. They
may possibly be triggered by a reaction to a trauma, ADF usually present as small and solitary dome-shaped lesions with a
collarete of slighty raised skin at the base. We report a rare case of fibrokeratoma of the heel, presenting as a large and
pedunculated nodule.

Clinical synopsis

A 50-year-old Brazilian man presented with a 12-year history of an asymptomatic pedunculated nodule on the right heel region
(Figs. 1 & 2). The growth had slowly enlarged over the years. The patient denied any previous local trauma.

Figure 1

Figure 2

Figure 3

On physical examination, the patient presented a 30 x 22 x 10 mm non-tender, skin colored, pedunculated firm nodule that protruded
from his right heel towards the sole (Figs. 1 & 2). At the base of the nodule there was a ring of yellow keratin (Fig. 3).
The clinical impression was cutaneous horn or fibrokeratoma. A shave excision was performed and the specimen was submitted
for histopathologic study. Microscopic exam revealed a polipoid lesion, with epidermal hyperplasia and focal spongiosis. The
bulk of the tumor consisted of collagen fibers perpendicularly arranged, accompanied by chronic inflammatory changes (Figs.
4 & 5). Elastic fibers were normal.

Figure 4

Figure 5

Figure 6

The diagnosis of acquired fibrokeratoma was confirmed. The patient had no recurrence two months after the surgical procedure
(Fig. 6).

Discussion

The name, acquired digital fibrokeratoma, was first coined by Bart et al. in 1968, who stated that the lesions resemble a
"rudimentary supernumerary digit [1]." It is a benign tumor, almost always solitary. It can be seen in adults and does not show spontaneous regression. In most
cases, ADF appears as a small solitary, painless, and skin colored lesion mainly on the fingers and toes, occasionally originating
from the proximal nail fold. The tumor rarely can affect the palms and soles [2]. In general, persistent minor trauma has been suggested as the trigger for the development of the lesion, particularly on
the digits [3].

There are a few reported cases of fibrokeratoma on the heel. Such tumors on the plantar surface have been recognized in the
past, but not described in detail. Verallo [4] in his description of 32 cases of acquired digital fibrokeratoma indicated that six were actually located on sites other
than digits, including palm and sole, but further detail of these nondigital fibrokeratomas were not given. The author suggests
that since not all those lesions are on the digits, the term, acquired fibrokeratoma, would be more appropriate. It was not
until Reed and Elmer [5] that the term acral was used to describe the location of acquired fibrokeratomas.

Fourteen years later, Cooper and Mackel [6] described a patient with a 30 mm diameter sessile tumor on the heel. Because it was tender and interfered with the patient's
normal activities it was excised; there was no recurrence after six months of follow up. The authors decided to drop the terms,
digital and acral, in describing the location of the lesion.

Spitalny and Lavery [7] described a 43-year-old Hispanic male with a painful, gigantic fibrokeratoma arising on the heel measuring 11 x 70 x 50
mm. As reported, the tumor was similar to fungiform papillae of the tongue and its appearance was reminiscent of the case
presented by Cooper and Meckel [6]. Jaiswal et al. [8] described the case of a 38-year-old man with an asymptomatic, 15 x 20 mm, bullet shaped, pedunculated, firm nodule on the
medial margin of left heel. The patient had a history of several repeated minor injuries prior to the onset of the tumor.
He was treated with excision with no evidence of recurrence in the following couple of years. In 2004, Bron et al. [9] reported a case of giant fibrokeratoma, measuring 30 x 15 mm on the left heel, in a 77-year-old patient. They performed
a shave excision of the lesion and the patient had no recurrence in one year of follow up.

Histologically, fibrokeratomas are benign fibroepithelial tumors marked by a hyperkeratotic and acanthotic epidermis with
thickened, often branching, rete ridges. The core of the lesion is formed by thick, interwoven bundles of collagen, predominantly
vertically oriented. Elastic fibers are usually present but are apt to be thin and sparse. Many tumors are highly vascular
[10]. Based on the uncommon site, the pedunculated shape, and the large dimensions of the presented tumor, we agree that the
name, acquired fibrokeratoma or acral fibrokeratoma, would be more appropriate than acquired digital fibrokeratoma.

Acknowledgments: We appreciate the language review by Lilian Bonilha Morais.